The Mentored Clinical Scientist Development Award will provide the opportunity to extend the applicant's intensive molecular virology training and develop an expertise in protein biochemistry and cellular biology. These skills will enable the applicant to become a fully independent research scientist and to address studies that dissect the molecular and genetic basis of viral infection and human disease. The mentor who will direct this training is an expert in herpes simplex virology. The candidate's career objective is to become a pediatrician- scientist who provides insights into viral pathogenesis which ultimately will improve the therapeutic and management decisions for patients with viral infections. Research interests of the applicant focus on the molecular and genetic basis for viral pathogenesis: specifically, how viruses evade intrinsic and immune host defense systems. This proposal examines how second-site mutations in avirulent herpesviruses enable progeny to reacquire their pathogenic potential and evade an intracellular host defense system, the interferon induced protein kinase (PKR). Studies have identified that a change in the kinetic expression of an HSV gene flanking the second site mutations (US11) contributes to the renewed pathogenicity of these viruses. These studies have not resolved a significant paradox: the early synthesis of US11 protein enables viral evasion of PKR but pre-made protein carried in with the virus is ineffective. The working hypothesis of this proposal is that while these functional differences in PKR inhibition may reflect inherent biochemical differences between the pre-made and synthesized US11, it is more likely that this reflects the relative ability of synthesized US11 to recruit accessory infected cell proteins. Biochemical techniques (chromatography, 2-D electrophoresis, in vivo phosphorylation) will be used to isolate and analyze virion-associated and synthesized US11. This will be followed by tests for functional differences using a PKR in vitro kinase assay. Affinity studies using both biochemical (immunoprecipitation, protein affinity) and genetic methods (yeast two hybrid system) will evaluate if US11 or PKR recruit participating infected cell proteins that modify the PKR pathway. An in vitro PKR kinase assay will test the functional significance of the identified proteins. Finally, biologic function will be evaluated by creating a cell line expressing the US11 and identified gene with an avirulent virus and examining for phenotypic changes.